The present disclosure relates generally to fuel systems for gas turbine engines. In particular, the present disclosure relates to fuel systems utilizing fuel flow to operate engine actuation systems.
In conventional fuel systems, a main fuel pump is used to deliver fuel to a fuel metering valve that provides fuel directly to fuel injectors in the combustion section of the engine. Additionally, some of the fuel flow from the main fuel pump is circulated through actuators that operate other engine or aircraft systems. Such a system is described in U.S. Pat. No. 4,487,016, which is assigned to United Technologies Corporation. In some systems, fuel flow is metered using a servo valve-controlled torque motor that provides fuel based on engine requirements for different speeds. Additionally, servo valve-controlled valves are used to regulate airflow to active clearance control systems and variable vane systems based on fuel flow. The servo valves utilize fuel flow from the main fuel pump to provide actuation. The main fuel pump needs to be sized at a minimum to provide flow to the servo valves and to the injectors at idle engine speed, and at a maximum to provide flow to the servo valves and to the injectors under transient engine conditions, such as during take-off. Thus, the main fuel pump must have a large capacity to accommodate the entire engine operating envelope and to provide fuel to other various aircraft systems. The large pump capacity produces inefficiencies in the engine, such as consuming excess system horsepower and generating waste heat. Furthermore, the servo valve-controlled actuators need to be sized to withstand the elevated pressures generated during transient conditions and the associated fatigue stress with such a wide operating envelope. There is, therefore, a need for a more efficient fuel and actuation system for gas turbine engines.